The present invention relates to an improved quick action keyless drill chuck.
Drill chucks for fitting to drilling machines and having the characteristics of a rapid hand applied gripping and release action without requiring the use of a chuck key, have been known in the art for many years. (The said key in fact, as currently known is in the form of a handled pinion). We know that keyless chucks call for a high degree of precision so as to provide operating characteristics which would be equivalent to those of chucks requiring a key, within the same catagory. For this reason, on the basis of technical operational equality, such as the capability of performing work of a similar nature, wear resistance, the level of precision in the work operation, mechanical life of the mechanism and other aspects, the cost of quick action keyless chucks has been considerably higher than that of the more traditional drill chucks which are provided with a chuck key. Consequently the user has had to pay a high price for the advantage of the ease of operation offered by a drill chuck not requiring the traditional chuck key. It follows logically that this reason has been a major inhibitor to the potential user who would buy the traditional type of drill chuck solely on account of its lower price.
The drill chuck mechanism which is disclosed in this present invention substantially alters this situation, relating, as it does to a keyless drill chuck, that is to say, self-gripping, which while offering a high quality of operation, has a relatively low cost, enabling it to be competitive with the traditional key operated chucks on the market and hence with the keyless type drill chucks known up to the present.
In addition the invention offers a further advantage in a better load resistance, that is to say it is capable of being subject to at least the same or even greater loads without danger of a breakage in the internal components, particularly of the thrust screw. Furthermore this keyless drill chuck weighs notably less than the keyless drill chucks known at present, a characteristic which is highly advantageous. While recent developments in technology have resulted in new materials in industry, permitting considerable weight reductions in the manufacture of drilling machines, the drill chucks fitted to the front extremity of these same machines have not undergone any significant development in this direction and consequently their disproportionate weight in relation to the machine results in a lack of equilibrium between the machine itself and the drill chuck weight located at its extremity. The drill chuck which is the object of this invention permits considerable progress to be achieved in this respect.
The reduction in the cost of manufacture together with the improved load resistance and the decrease in the weight are the result of the novel elements in the structure of the chuck which, while serving the same ultimate purposes as the currently known keyless chucks, is composed of a number of structural components which are both easy and cheap to manufacture.
The general structure of the currently known keyless drill chucks comprises the following components:
(a) An upper cylindrical outer half-body. PA1 (b) A lower conical outer half-body. This being a conical sleeve fitted by a screw thread to the item (a) above. PA1 (c) A central body. PA1 (d) A thrust screw which is fitted by a screw thread into an axial internal orifice provided in the above mentioned central body (c). PA1 (e) Three chuck jaws which engage, by hooking in mechanically to the leading edge of the above mentioned thrust screw (d). PA1 (f) A guide-cage which provides guidance for the three jaws (e) in the course of their movement for gripping, (forward movement mutually closing in together) and releasing (backward movement mutually separating). This guide-cage (f) is provided with a relatively long skirt at the rear surrounding its rear orifice. PA1 (g) Ball bearings. PA1 (h) Bearing track. PA1 (i) Flange ring, provided with a locking screw for retaining it. PA1 (j) A connecting piece between the guide-cage (f) and the lower conical outer half-body (b).
The technology of the keyless drill chuck of which the more fundamental components have been described above is thoroughly known to the specialists in the art, as is also the mode of operation and therefore the detailed description will not be given in this specification, so as not to make it unnecessarily lengthy. However reference will be made to certain aspects of the mode of operation where it is considered that this would contribute to a better understanding of the invention.
The high cost of manufacture of this keyless drill chuck as currently known, is due in part to the fact that some of its components, particularly the central body (c), have to be relatively long, this affecting as a consequence the length of the components directly connected to the central body, resulting in the high weight of these components and in a large area of the surfaces which require machining. This feature, referred to above is easily appreciated on consideration of the high cost of the materials used in their raw state as well as the high cost of machining. Another factor contributing to the high price of the complete drill chuck is that in the aforementioned known chuck a large number of its components require contact surfaces to be finished to an extremely high standard.
Another object of the invention is to disclose a complementary device especially applicable to the said drill chuck in such cases as it is required to subject the drill, apart from its usual rotary movement, to a reciprocating movement of percussion.
It is common knowledge that the known keyless drill chucks are not capable on their own, (with their simplified basic structure) of maintaining continuously and efficiently a tight grip on the drill when used with a percussion movement. This is because the self gripping tendency on the drill depends in every case on the continuous resistance encountered by the drill in its rotary movement as it penetrates the material being drilled. In the case of a percussion drill there are moments during which the drill is no longer meeting resistance; this occuring during the phase of the hammer operation in which the drill withdraws longitudinally. So as to resolve this problem the fundamental structure of the known keyless drill chucks is extended by means of a complementary device designed so as to ensure that the grip on the drill is maintained during the percussion operation.
These complementary devices, as currently known, possess three basic major disadvantages: they are structurally complex; they are costly to manufacture; and they require the operator to undertake special measures to connect and to disconnect them in fitting them to the drill chuck. Also the structural complexity peculiar to these known devices gives rise to a major increase in the weight of the drill chuck and also to a considerable increase in the length of the said chuck. All the above disadvantages are elliminated by the use of the simple and efficient device, permanently in place, (that is, requiring no action on the part of the operator), to which this present invention patent relates.